feat: render per-vertex color triangle

- Add shader class for vertex/fragment program compilation
- Add vao class for vertex array object management
- Render RGB gradient triangle with interpolated vertex colors

cbt/opengl/vao.hpp

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "glad/glad.h"
+
+namespace cbt::opengl {
+
+class vao {
+    GLuint m_id = 0;
+
+public:
+    vao();
+    ~vao();
+
+    vao(const vao&) = delete;
+    vao& operator=(const vao&) = delete;
+
+    vao(vao&& other) noexcept;
+    vao& operator=(vao&& other) noexcept;
+
+    auto bind() const -> void;
+    auto unbind() const -> void;
+    auto id() const -> GLuint;
+    auto valid() const -> bool;
+};
+
+}